The present invention is related to the design of MOS transistors and, in particular, to the design of MOS transistors operating in the RF frequency region.
Current semiconductor processing technologies have enabled the reduction of sizes of transistors with critical dimensions below 0.25 μm. Critical dimensions are now approaching 0.18 μm and even more aggressive technologies are considering critical dimensions of 0.13 μm. The operating frequencies of the resulting integrated circuits have risen to such an extent that MOS (Metal-Oxide-Semiconductor) integrated circuits are being used for RF (Radio Frequency) applications.
However, at high frequencies the transistors operate less efficiently in some applications. This is especially true when the MOS transistor is used in a receiving circuit, which is required to have high linearity and low-noise. The AC output conductance and the AC output capacitance of the transistor are adversely affected. The output conductance increases with frequency and the output capacitance becomes highly dependent upon the device's bias. An increase in output conductance results in reduced gain and bias dependency results in added distortion. Additionally, in a low-noise amplifier circuit, unintended and undesirable circuit feedback voltage may be induced from the back gate-to-source connection.
Therefore, an MOS transistor for RF operations in which the shortcomings above are solved or substantially alleviated is desirable. The present invention provides for such an MOS transistor, which is highly suitable for operation with RF circuits.